Golf ball

ABSTRACT

An object of the present invention is to provide a golf ball having an individualized and improved appearance by imparting the luster, without lowering durability and a color developing property of the paint film and/or the mark. Another object of the present invention is to provide a golf ball having an improved visibility, which the mark should inherently provide. The present invention provides a golf ball comprising a golf ball body, a mark formed on the golf ball body, a paint film coating the golf ball body and the mark, wherein the mark and/or the paint film contains a luster material, wherein the luster material has a core material having a transparent base and a first transparent layer formed on the transparent base; and at least one composite layer formed on the core material and consisting of a second transparent layer having a lower refractive index than the first transparent layer, and a third transparent layer having a higher refractive index than the second transparent layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a golf ball, more particularly to a technique which improves the appearance of the golf ball.

2. Description of the Related Art

A golf ball is normally colored white, but there has been an increasing demand for a golf ball with an enhanced quality and an individualized appearance. In response to such a demand, a golf ball having a paint film or a cover to which the luster is imparted has been proposed.

For example, Japanese patent publication No. H06-170013A discloses a golf ball containing a pigment developing color by an interferential action of reflected lights in a paint layer on a ball surface or a ball body, the hue of which changes depending on an angle from which it is viewed. Japanese patent publication No. 2004-166719A proposes a golf ball provided with a mark formed on a surface of the golf ball body and a transparent covering layer covering the mark, wherein the transparent covering layer comprises a base resin and a luster material of a glass flake having a surface thereof covered with a metal oxide, and covers the mark that has a color tone satisfying L<=40 when represented by Lab system. Since the transparent covering layer covering the mark includes the luster material, it is possible to provide the golf ball with luster without lowering durability of the mark and the paint film itself. Japanese patent publication No. 2005-52510A discloses a golf ball comprising a core and a cover having two or more layers covering the core, wherein a base material of an outermost layer cover of the cover is a thermoplastic resin in which 0.2 to 5 parts by mass of a cholesteric liquid crystal polymer is included based on 100 parts by mass of the thermoplastic resin, and wherein a base material of an inner cover adjacent to the outermost layer cover is a thermoplastic resin in which 1 part by mass or less of titanium oxide and 1 part by mass or less of a fluorescent pigment are included respectively based on 100 parts by mass of the thermoplastic resin.

A golf ball generally has printed marks such as letters, numbers and drawings to represent a brand name, a play number or the like on a surface of the golf ball body. In recent years, golfers tend to prefer the golf ball having the luxurious or unique appearance. In order to satisfy the preference, there are provided golf balls where the mark having the luster is formed by blending the metal powder or the like into the ink composition for printing the mark.

For example, Japanese patent publication No. H11-114093 A discloses a golf ball where the mark is printed with the ink composition comprising a pigment and a metal powder. Japanese patent publication No. H11-319147 A discloses a golf having the mark of the predetermined drawings. The mark is printed with the ink composition comprising the luster-developing component. Japanese patent publication No. 2003-210617 A discloses a golf ball where the mark is printed with the ink composition comprising a metal powder having a resin coating on the surface thereof and a pigment as an essential component. Japanese patent publication No. 2007-136171 A discloses a golf ball having a mark formed from an ink that comprises a rare-earth element oxide or a rare-earth elements composite oxide exhibiting photochromism where color changes under a light having a special wave length. Japanese patent publication No. 2001-131489 A discloses a paint composition containing a luster material consisting of bismuth oxychloride crystal as a paint composition providing a silky tone in addition to the luster(brilliance).

SUMMARY OF THE INVENTION

Since the luster material consisting of a liquid crystal polymer has a spiral structure, there is a problem that the luster is lowered due to the change of pitches depending on the temperature. Further, the use of the luster material consisting of the liquid crystal polymer tends to lower the durability of the cover.

In general, materials such as metal powders have poor dispersibility to the ink resin, which causes problems that it is difficult to prepare the ink composition or that the transfer of the ink to the silicone pad becomes poor when printing marks in a pad stamp method. The golf ball mark must have the durability enough to endure the repeated impacts. However, since the dispersibility of the metal powders is poor, the mark becomes too brittle to exhibit the sufficient durability. In addition, if the mark is provided with the luster, it is possible to enhance the visibility of the mark from a long distance as well as impart the luxurious appearance to the mark. Further, if the mark has durability, the luster and visibility of the mark hardly change with time, and thus the golf ball maintains an original appearance.

Moreover, the conventional luster material used in the paint film and the ink composition do not provide the luster sufficiently. If the conventional luster materials containing a metal as a base material are used in the paint film and the ink composition, since the luster materials have low transparency, the color developing of the mark and the golf ball cover tends to be low. In order to solve this problem, there exists a need for further improvement, in view of the design of the golf ball and the visibility of the mark.

The present invention has been achieved in view of the above circumstances. An object of the present invention is to provide a golf ball having an individualized and improved appearance by imparting the luster, without lowering durability and a color developing property of the paint film and/or the mark. Another object of the present invention is to provide a golf ball having an improved visibility, which the mark should inherently provide.

The present invention, which has solved the above problem, provides a golf ball comprising a golf ball body, a mark formed on the golf ball body, a paint film coating the golf ball body and the mark, wherein the mark and/or the paint film contains a luster material, wherein the luster material has a core material having a transparent base and a first transparent layer formed on the transparent base; and at least one composite layer formed on the core material and consisting of a second transparent layer having a lower refractive index than the first transparent layer, and a third transparent layer having a higher refractive index than the second transparent layer.

According to the present invention, it is possible to obtain a golf ball having an individualized and improved appearance by imparting the luster, without lowering durability of the paint film and/or the mark. Further, it is possible to provide a golf ball having an enhanced visibility which the mark should inherently provide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view schematically showing a luster material used in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to a golf ball comprising a golf ball body, a mark formed on the golf ball body, a paint film coating the golf ball body and the mark, wherein the mark and/or the paint film contains a luster material, wherein the luster material has a core material having a transparent base and a first transparent layer formed on the transparent base; and at least one composite layer formed on the core material and consisting of a second transparent layer having a lower refractive index than the first transparent layer, and a third transparent layer having a higher refractive index than the second transparent layer. In the present invention, “transparent” does not only include “perfectly transparent” but also “translucent.”

First, the luster material used in the present invention will be explained in reference to the FIG. 1. FIG. 1 schematically shows a cross sectional structure of the luster material used in the present invention.

As shown in FIG. 1, the luster material used in the present invention at least comprises a core material 3 consisting of a transparent base 1 and a first transparent layer 2, and a composite layer 6 consisting of a second transparent layer 4 and a third transparent layer 5. Use of the luster material having such a multi-layered structure increase faces (interface between each layer) where the incident light reflects, and thus the obtained mark and the paint film have high glittering property. Further, the luster material develops the color by the interference of the reflecting lights reflected at the each face and changes color depending on the angle from which they are viewed, because the layers having different refractive index are laminated. Accordingly, use of this luster material gives a multi-color due to called “a flip-flop effect” where the color tone changes depending on the viewing angles and light source, and thus a golf ball having an excellent design is obtained.

Further, since the base material and all the layers of the luster material used in the present invention have high transparency, the pigment develops the color well. That is, if the luster material is used for the mark, the pigment contained in the ink composition develops the color well, and thus the visibility of the mark is further improved. If the luster material is used for the paint film, the brightness and the vividness are further improved, without deteriorating the brightness of the mark and the cover, even if the mark and the cover has a bright color. It is noted that since a light cannot transmit the luster material where the metal core is coated with a metal oxide, the mark or the cover has a dull color and thus the color development becomes lowered. Especially, in the present invention, the base material and all the layer of the luster material have high transparency, the luster material becomes substantially transparent depending on the angle from which they are viewed. Due to this, the obtained paint film is excellent in the transparency (color development), compared to the luster material having a low transparent or opaque base material or coating layer.

The luster material comprises a core material having the transparent base and the first transparent layer formed on the transparent base, and at least one composite layer formed on the core material and consisting of the second transparent layer and the third transparent layer. Multiple composite layers may be formed on the core material, but if each one layer of the first transparent layer, the second transparent layer and the third transparent layer is formed, the effect of the present invention is obtained, thus single composite layer is preferable in view of economic efficiency.

In one preferable embodiment of the luster material, the first transparent layers are directly formed on the both faces of the transparent base, and the second transparent layers are directly formed on the first transparent layers, and the third transparent layers are directly formed on the second transparent layers. That is, the luster material preferably has a seven-layered structure of the third transparent layer/the second transparent layer/the first transparent layer/the transparent base/the first transparent layer/the second transparent layer/the third transparent layer, as shown in FIG. 1

The transparent base is not limited, as long as it is a transparent platelet, and includes, for example, inorganic materials such as a glass flake and mica; transparent resins such as a polycarbonate resin, an acrylic resin, an epoxy resin. Among them, the glass flake is preferable, and the glass flake composed of borosilicate glass is more preferable. The transparent base preferably has a light transmission of at least 75%.

Materials constituting the first transparent layer and the third transparent layer include, for example, anatase-type titanium dioxide, rutile type titanium dioxide, iron oxide, zirconium dioxide, zinc oxide, zinc sulfide, bismuth oxychloride, or the like, preferably titanium oxide (TiO₂). The same material is preferably used for the first transparent layer and the third transparent layer, although different materials may be used for the first transparent layer and the third transparent layer. Material constituting the second transparent layer includes, for example, silicon dioxide, magnesium fluoride, aluminum oxide or the like, preferably include silicon dioxide (SiO₂). As the materials constituting each layer, any material can be selected, if a difference of the refractive index between the adjacent layers is at least 0.2, preferably at least 0.6. That is, the material constituting the second transparent layer preferably has a refractive index which is lower than the refractive index of the materials constituting the first transparent layer and the third transparent layer by at least 0.2.

In a more preferable embodiment of the luster material used in the present invention, the first transparent layer consisting of TiO₂ is directly formed on the both faces of the glass flake of borosilicate glass, and the second transparent layer consisting of SiO₂ is directly formed on the first transparent layer, and the third transparent layer consisting of TiO₂ is directly formed on the second transparent layer. This luster material can be prepared by coating a glass flake of borosilicate glass with TiO₂, SiO₂, and TiO₂ in this turn by a sol-gel method.

The thickness of the first transparent layer, the second transparent layer and the third transparent layer can be adjusted appropriately depending upon the desired color (interference color), but preferably ranges from about 40 nm to about 250 nm.

The luster material preferably has an average particle size of 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more and preferably has an average particle size of 300 μm or less, more preferably 200 μm or less, even more preferably 150 μm or less. If the luster material has the average particle size of 5 μm or more, the glittering effect due to the luster material becomes larger, while if the luster material has the average particle size of 300 μm or less, the durability of the obtained mark and the paint film is further improved. In the present invention, “average particle size” means “number-average particle size”.

The luster material preferably has an average thickness of 0.5 μm or more, more preferably 1 μm or more, and has an average thickness of 5 μm or less, more preferably 3 μm or less. If the luster material has an average thickness of 0.5 μm or more, the glittering effect due to the luster material becomes larger, while if the luster material has an average thickness of 5 μm or less, the durability of the obtained mark and the paint film is further improved and the golf ball can maintain a good appearance for a long term.

Specific examples of the luster material used in the present invention are, for example, “Firemist (registered trade mark) Colormotion Ruby,” “Firemist Colormotion Blue Topaz,” “Firemist Colormotion Amethyst,” or “Firemist Colormotion Aquamarine,” available from BASF Corporation.

The golf ball of the present invention comprises a golf ball body, a mark formed on the golf ball body, a paint film coating the golf ball body and the mark, wherein the mark and/or the paint film contains the luster material.

That is, since at least one of the mark and the paint film contains the luster material, the golf ball having an excellent appearance is obtained. Specific embodiments include an embodiment where only the mark contain the luster material, an embodiment where only the paint film coating the golf ball body contains the luster material, and an embodiment where both of the mark and the paint film coating the golf ball body contain the luster material.

In the following, the mark will be explained. The mark can be formed from an ink composition containing a pigment.

In the case that the ink composition contains the luster material, the ink composition preferably contains the luster material in an amount of 1 mass % or more, more preferably 1.5 mass % or more, even more preferably 2.0 mass % or more, and preferably contains the luster material in an amount of 30 mass % or less, more preferably 25 mass % or less, even more preferably 20 mass % or less. If the amount is 1 mass % or more, the luster of the mark is further improved. If the amount is 30 mass % or less, the impact resistance of the mark is further improved, because the amount of the luster material contained in the ink composition is not too much.

The ink composition contains a pigment, irrespective of containing the luster material. The pigment contained in the ink composition is a pigment used for coloring an article and includes a white or colored inorganic compound or organic compound that are not dissolved into a medium such as water, oil, and solvents. The pigment is not limited, as long as it imparts a desired color to the mark. The pigment, for example, includes an inorganic pigment and an organic pigment. Examples of the pigments are a black pigment such as carbon black; a white pigment such as titanium oxide; blue pigments such as ultramarine blue, cobalt blue, and phthalocyanine blue; violet pigments such as anthraquinone violet, dioxane violet, and methyl violet; yellow pigments such as titanium yellow (20 TiO₂—NiO—Sb₂O₃), litharge (PbO), chrome yellow (PbCrO₄), yellow iron oxide (FeO(OH)), cadmium yellow, pigment yellow-1, and pigment yellow-12; and red pigments such as red iron oxide (Fe₂O₃), red lead oxide (Pb₃O₄), molybdenum red, and cadmium red, pigment red-3, pigment red-57 and pigment orange-13. These pigments may be used either alone or as a mixture of two or more of them.

The ink composition preferably contains the pigment in an amount of 0.5 mass % or more, more preferably 1 mass % or more, and preferably contains the pigment in an amount of 20 mass % or less, more preferably 10 mass % or less. If the amount is 0.5 mass % or more, the color becomes strong due to the pigment and the mark becomes vivid. If the amount is 20 mass % or less, the glittering effect due to the luster material becomes better, because the color of the pigment is not too strong.

In the present invention, it is preferable to balance the content of the pigment with that of the luster material in the ink composition, since the balance of the impact resistance, visibility and luster of the mark can be adjusted. The content ratio of the luster material to the pigment (luster material[mass %]/pigment [mass %]) is preferably 0.1 or more, even more preferably 0.5 or more, more preferably 1 or more, and is preferably 50 or less, more preferably 40 or less, even more preferably 30 or less. If the ratio is 0.1 or more, the content ratio of the luster material to the pigment is high, and the glittering effect becomes stronger. If the ratio is 50 or less, the content of the luster material contained in the ink composition is not too high, and thus the impact resistance of the mark becomes better.

The ink composition of the present invention preferably contains a base resin in addition to the luster material and the pigment, and may further contain an ultraviolet absorber, a light stabilizer, a solvent, a plasticizer and other additives where necessary.

The base resin includes a resin conventionally used for the ink composition for the golf ball mark. The base resin, for example, without limitation, includes a polyester resin, an epoxy resin, a soluble nitrocellulose, an acrylic resin, a vinyl chloride-vinyl acetate copolymer, an urethane resin, a polyamide resin or the like. These resins may be used solely or in combination of at least two of them. Among them, the epoxy resin, the polyester resin or the soluble nitrocellulose is preferable, because they provide a good adhesion. In the case that the epoxy resin is used as the base resin, polyisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, or tolylene diisocyanate are preferably used as a curing agent.

The ink composition preferably contains the base resin in an amount (solid content) of 15 mass % or more, more preferably 17 mass % or more, even more preferably 20 mass % or more, and preferably contains the base resin in an amount of 50 mass % or less, more preferably 45 mass % or less, even more preferably 42 mass % or less, even more preferably 40 mass % or less. If the content of the base resin is 15 mass % or more, the adhesion of the mark to the golf ball body becomes better, while if the content is 50 mass % or less, the blending amount of the solvent and the pigment becomes relatively high, and thus the color of the resultant mark becomes strong and the visibility is further improved.

The ultraviolet absorber or the light stabilizer conventionally used for the ink composition for the golf ball mark can be used in the present invention. Illustrative examples include ultraviolet absorbers such as salicylic acid derivatives, benzophenone derivatives, benzotriazole derivatives, cyanoacrylate derivatives, triazine derivatives, nickel complexes and light stabilizer such as hindered amine derivatives.

Examples of the salicylic acid derivative include phenyl salicylate, p-t-butylphenyl salicylate, p-octylphenyl salicylate and the like. Examples of the benzophenone derivative include 2,4-dihydroxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2-dihydroxy-4,4′-methoxybenzophenone and the like. Examples of the benzotriazole derivative include 2-(2′-hydroxy-5′-methylphenyl)benzotriazole, 2-(2′-hydroxy-5′-t-butylphenyl)benzotriazole, 2-(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazole, 2-[2-hydroxy-3,5-bis(α,α′-dimethylbenzyl)phenyl]-2H-benzotriazole, 2-(5-methyl-2-hydroxyphenyl)benzotriazole. Examples of the cyanoacrylate derivative include 2-ethylhexyl-2-cyano-3,3′-diphenyl acrylate, ethyl-2-cyano-3,3′-diphenyl acrylate. Examples of the triazine derivative include 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5[(hexyl)oxy]-phenol, 2,4-bis(2-hydroxy-4-butyroxyphenyl]-6-(2,4-bis-butyroxyphenyl)-1,3,5-triazine and 2-[4-[(2-hydroxy-3-(2′-ethyl)hexyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine. Specifically, the benzophenone based ultraviolet absorber includes “Sumisoap 130,” “Sumisoap 140” or the like manufactured by Sumitomo Chemical Co., Ltd.; the benzotriazole based ultraviolet absorber includes “TINUVIN 234”, “TINUVIN 900”, “TINUVIN 326”, “TINUVIN P” or the like manufactured by Ciba Specialty Chemicals plc.; and the cyanoacrylate based ultraviolet absorber includes “Uvinul N-35” or the like manufactured by BASF Corporation. The triazine based ultraviolet absorber includes “TINUVIN 1577”, “TINUVIN 460”, “TINUVIN 405” or the like manufactured by Ciba Specialty Chemicals plc. These ultraviolet absorbers may be used individually or in combination of two or more. The ultraviolet absorbers that can be used in the present invention are not limited to the above examples, and any ultraviolet absorber that is publicly known can be used in the present invention.

Examples of the hindered amine light stabilizer include bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate], and 1-[2-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]ethyl]-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]-2,2,6,6-tetramethylpiperidine. Specific examples include trade name “Sanol LS-2626” and trade name “TINUVIN 144” manufactured by Ciba Specialty Chemicals plc.

The ink composition preferably contains the ultraviolet absorber in an amount of 0.01 mass % or more, more preferably 0.1 mass % or more, even more preferably 1.0 mass % or more, and preferably contains the ultraviolet absorber in an amount of 10 mass % or less, more preferably 5 mass % or less. The ink composition preferably contains the light stabilizer in an amount of 0.1 mass % or more, more preferably 0.2 mass % or more, even more preferably 0.3 mass % or more, and preferably contains the light stabilizer in an amount of 10 mass % or less, more preferably 9 mass % or less, even more preferably 8 mass % or less. If the ink composition contains the ultraviolet absorber and the light stabilizer, the effect of blocking the ultraviolet light or improving the stability against the light can be obtained. Further, if the amount thereof is too large, the amount of the other component becomes relatively low, and thus the color of the resultant mark is getting tint, or the impact resistance or abrasion resistance of the mark may be lowered.

As the solvent, a solvent conventionally used for the ink composition for the golf ball mark can be employed. The solvent includes, without limitation, cyclohexanone, acetylacetone, propyleneglycolmonomethyletheracetate, methoxymethylbutylacetate, ethylacetate, an aromatic hydrocarbon, or a mixture of at least two of them.

The ink composition preferably contains the solvent in an amount of 20 mass % or more, more preferably 25 mass % or more, even more preferably 30 mass % or more, and preferably contains 60 mass % or less, more preferably 55 mass % or less. If the content of the solvent is 20 mass % or more, the viscosity of the ink composition is not so high that the print-workability becomes better, while if the content of the solvent is 60 mass % or less, it can take a shorter time to dry the mark after printed, and the productivity of the golf ball becomes better.

The additives include, for example, a flatting agent, a defoamer, an antisettling agent or the like. Examples of the flatting agent are colloidal silica, a low density polyethylene particle, or a medium density polyethylene particle. As the defoamer, preferred is methylsiloxane. The content of the flatting agent contained in the ink composition is preferably, but not limited to, from 0.5 mass % to 5 mass %. The content of the defoamer contained in the ink composition is preferably from 0.5 mass % to 5 mass %. As the antisettling agent, anhydrous silica, an acrylic viscosity modifier, oxidized polyethylene, activated polyamide wax, and bentonite or the like can be used. The content of the antisettling agent is preferably from 0.01 mass % to 3.0 mass %. As the antisettling agent, preferred is aerosil available from NIPPON AEROSIL Co., LTD.

The ink composition used in the present invention preferably contains a non-volatile component in an amount of 20 mass % or more, more preferably 30 mass % or more, even more preferably 35 mass % or more and preferably contains a non-volatile component in an amount of 70 mass % or less, more preferably 60 mass % or less, even more preferably 55 mass % or less. If the content of the non-volatile component is 20 mass % or more, the occurrence of “color shading” or “transparency” of the mark can be avoided. On the other hand, if the content is 70 mass % or less, the viscosity of the ink composition does not become too high, and the printability becomes better.

Each content of the luster material, the pigment, the solvent, the base resin, and other additives is appropriately determined from the ranges mentioned above so that the total amount of the ink composition becomes 100 mass %.

Next, the paint film will be explained. The paint film may be formed in a manner that it coats the golf ball body and the mark. The paint film may be what is called a clear paint layer containing a resin component without another pigment, or may be what is called an enamel paint layer containing a resin component and a pigment. But it is necessary that the paint film is clear.

In the case that the paint film contains the luster material, a content of the luster material in the paint film is not particularly limited, but it is preferably 0.05 part by mass or more, more preferably 0.1 part by mass or more, even more preferably 0.5 part by mass or more and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less based on 100 parts by mass of the resin component. If the content of the luster material is 0.05 part or more with respect to 100 parts by mass of the resin component, the glittering effect of the paint film becomes larger, while if the content is 20 parts by mass or less, the impact resistance of the paint film becomes better.

The paint film contains a resin component, irrespective of containing the luster material. The resin component constituting the paint film is not particularly limited, and an acrylic resin, an epoxy resin, a polyurethane resin, a polyester-based resin, a cellulose-based resin or the like may be used, but a two-component curing type polyurethane resin described later is preferably used. If the two-component curing type polyurethane resin is used, a paint layer which is further excellent in the impact resistance can be obtained.

The two-component curing type polyurethane resin is a polyurethane resin obtained by reacting and curing a base resin with a curing agent. Such examples include one obtained by curing a base resin containing a polyol component with a polyisocyanate compound or a derivative thereof.

The base resin containing the polyol component preferably contains a specific urethane polyol as described in the following. The urethane polyol is synthesized by a reaction between a polyisocyanate and a polyol. The polyisocyanate used for the synthesis is not particularly limited as long as it has two or more isocyanate groups. Such examples include an aromatic polyisocyanate such as 2,4-toluene diisocyanate, 2,6-tolylene diisocyanate, the mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), and paraphenylene diisocyanate (PPDI); and an alicyclic or aliphatic polyisocyanate such as 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenated xylylenediisocyanate (H₆XDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), norbornene diisocyanate (NBDI). These may be used either alone or as a mixture of at least two of them. Among them, in view of weather resistance, a non-yellowing type polyisocyanate such as TMXDI, XDI, HDI, H₆XDI, IPDI, H₁₂MDI, and NBDI is preferably used. The polyisocyanate may be also used as a curing agent for curing the urethane polyol.

The polyol used for preparing the urethane polyol is not particularly limited as long as it has a plurality of hydroxyl groups. Such examples include a polyol having a low-molecular weight and a polyol having a high molecular weight. Examples of the polyol having a low-molecular weight include a diol such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; and a triol such as glycerin, trimethylol propane, and hexanetriol. Examples of the polyol having a high molecular weight include a polyether polyol such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), polyoxytetramethylene glycol (PTMG); a condensed polyester polyol such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA); a lactone polyester polyol such as poly-ε-caprolactone (PCL); a polycarbonate polyol such as polyhexamethylene carbonate; an acrylic polyol and the like. Among the polyols described above, a polyol having a weight average molecular weight of 50 to 2,000, particularly a polyol having a weight average molecular weight of about 100 to 1,000 is preferably used. These polyols may be used either alone or as a mixture of at least two of them.

The urethane polyol is a polyol wherein a urethane bond is formed by a reaction between the polyisocyanate and a polyol, having a hydroxyl group at a terminal thereof. Herein, a ratio of the urethane bonds in the urethane polyol is preferably 0.1 mmol to 5 mmol in 1 g of the urethane polyol. A ratio of the urethane bonds is related to rigidity of the paint film to be formed, and if it is 0.1 mmol/g or more, urethane concentration of the paint film to be formed becomes so high that abrasion-resistance may become good. On the other hand, if it is 5 mmol/g or less, the paint film does not become so hard that the flexibility of the paint film with the deformation of the golf ball body becomes good and the impact resistance of the paint film is improved.

A weight average molecular weight of the urethane polyol is preferably 4,000 or more, more preferably 4,500 or more, and preferably less than 10,000, more preferably 9,000 or less. If the urethane polyol has a weight average molecular weight of 4,000 or more, it takes a shorter time to dry, so that workability and productivity becomes higher. On the other hand, if the urethane polyol has a molecular weight of less than 10,000, the hydroxyl value of the urethane polyol becomes relatively large, so that an reaction amount after coating becomes large, and thus adhesion to a base is further improved. Additionally, if a weight average molecular weight is 9,000 or less, a dense paint film (or a clear paint layer) which is less in lowering of adhesion even in a state of being wet in water can be formed.

A hydroxyl group value of the urethane polyol is preferably 15 mgKOH/g or more, more preferably 73 mgKOH/g or more, and preferably 130 mgKOH/g or less, more preferably 120 mgKOH/g or less. If the hydroxyl group value is 15 mgKOH/g or more, a reaction amount to the curing agent becomes larger, and thus adhesion strength to the ball body is further improved. On the other hand, if it is 130 mgKOH/g or less, a reaction with the curing agent does not require a long time, and a drying time becomes shorter to give a higher productivity. Also, the cracking hardly occurs at the time of impact.

The urethane polyol as described above can be obtained by reacting a polyol and a polyisocyanate which are to be raw materials in such a proportion that the hydroxyl groups of the polyol component is in excess relative to the isocyanate groups of the polyisocyanate component by molar ratio. In the above described reaction, a solvent or a catalyst (e.g., dibutyl tin dilaurylate) publicly known for use in a urethane reaction may be used. A ratio of the urethane bond may be adjusted by adjusting a molecular weight of the polyol which is to be a raw material, a blending ratio of the polyol and the polyisocyanate and the like.

The polyol component constituting the base resin is preferably the specific urethane polyol itself; that is, preferably, the base resin is substantially the specific urethane polyol, but may include a polyol which is compatible with the urethane polyol and devoid of the urethane bond, in addition to the urethane polyol. In such a case, the polyol devoid of the urethane bond is not particularly limited, and the above-mentioned raw material polyol for synthesizing the urethane polyol may be used. If the base resin contains a polyol devoid of the urethane bond, a content of the urethane polyol in the base resin is preferably 50 mass % or more, more preferably 80 mass % or more. If the content of the urethane polyol in the base resin is 50 mass % or more, the content of the urethane polyol becomes relatively high, so that a drying time becomes shorter.

Besides the abovementioned base resin or the like, the paint film may further contain an additive which is included in a paint for a conventional golf ball such as an ultraviolet absorber, an antioxidant, a light stabilizer, a fluorescent brightener, an antiblocking agent, and a pigment.

The ultraviolet absorber includes, for example, without limitation, salicylic acid derivatives, benzophenone derivatives, benzotriazole derivatives, cyanoacrylate derivatives, triazine derivatives, nickel complexes or the like.

Specifically, the benzophenone based ultraviolet absorber includes “Sumisoap 130,” “Sumisoap 140” or the like manufactured by Sumitomo Chemical Co., Ltd.; the benzotriazole based ultraviolet absorber includes “TINUVIN 234”, “TINUVIN 900”, “TINUVIN 326”, “TINUVIN P” or the like manufactured by Ciba Specialty Chemicals plc.; and the cyanoacrylate based ultraviolet absorber includes “Uvinul N-35” or the like manufactured by BASF Corporation. The triazine based ultraviolet absorber includes “TINUVIN 1577”, “TINUVIN 460”, “TINUVIN 405” or the like manufactured by Ciba Specialty Chemicals plc.

The light stabilizer preferably includes, for example, without limitation, hindered amine light stabilizers. Specific examples include trade name “Sanol (registered trade name) LS-700,” “Sanol LS-770P,” “Sanol LS-765,” “Sanol LS-292,” “Sanol LS-2626,” “Sanol LS-744,” “Sanol LS-944” manufactured by Ciba Specialty Chemicals plc.

The fluorescent brightener preferably includes, without limitation, “Ubitex (registered trade name) OB” available from Ciba Specialty Chemicals plc.

The paint composition is explained based on a solvent born system. However, the water born or aqueous paint can be also used in the present invention. For example, the two component curing type aqueous paint containing an aqueous polyol such as an aqueous acrylic polyol and aqueous urethane polyol and an aqueous polyisocyanate can be used. The water born or aqueous paint is disclosed in U.S. Pat. No. 7,371,193 and U.S. Pat. No. 7,387,821 and U.S. Patent Publication No. 2005/082661 A1, which is incorporated in its entirety by reference herein.

The golf ball of the present invention has no limitation on its structure and includes solid golf balls such as a one-piece golf ball, a two-piece golf ball, a multi-piece golf ball comprising at least three layers, and a wound-core golf ball. The present invention can be applied for all types of the golf ball.

In the following, the method for preparing the golf ball of the present invention will be explained based on the embodiment of the two-piece golf ball, but the present invention is not limited to the two-piece golf ball and the process explained below. The present invention can employ any core which is well-known as the core for the two-piece golf ball. The core of the two-piece golf ball, for example, without limitation, is preferably formed by heat pressing a core rubber composition. The core rubber composition preferably contains a base rubber, a co-crosslinking agent, a crosslinking initiator, a filler, an antioxide or the like. The base rubber preferably includes a natural rubber and/or a synthetic rubber. Examples of the base rubber are butadiene rubber (BR), ethylene-propylene-diene terpolymer (EPDM), isoprene rubber (IR), styrene-butadiene rubber (SBR), and acrylonitrile-butadiene rubber (NBR). Among them, butadiene rubber, particularly cis-1,4-polybutadiene, is preferable in view of its superior repulsion property. Typically preferred is the high cis-polybutadiene rubber having cis-1,4 bond in a proportion of not less than 40%, more preferably not less than 70%, even more preferably not less than 90%.

As the crosslinking initiator, an organic peroxide is preferably used. Examples of the organic peroxide for use in the present invention are dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Among them, dicumyl peroxide is preferable. The amount of the organic peroxide to be blended in the core rubber composition is preferably not less than 0.3 part by mass, more preferably not less than 0.4 part by mass, and preferably not more than 5 parts by mass, more preferably not more than 3 parts by mass based on 100 parts by mass of the base rubber. If the content is 0.3 part or more by mass, the core does not become too soft, and the resilience becomes better, and if the content is 5 parts or less by mass, the core does not become too hard and the shot feeling becomes better.

The co-crosslinking agent used in the present invention includes, for example, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metal salt thereof. As the metal forming the metal salt of the α,β-unsaturated carboxylic acid, a monovalent or divalent metal such as zinc, magnesium, calcium, aluminum and sodium is preferably used. Among them, zinc is preferable, because it can impart the higher repulsion property to the golf ball. Specific examples of the α,β-unsaturated carboxylic acid or a metal salt thereof are acrylic acid, methacrylic acid, zinc acrylate, and zinc methacrylate.

The amount of the co-crosslinking agent to be blended in the rubber composition is preferably not less than 10 parts by mass, more preferably not less than 15 parts by mass, even more preferably not less than 20 parts by mass, and preferably not more than 55 parts by mass, more preferably not more than 50 parts by mass, even more preferably not more than 48 parts by mass based on 100 parts by mass of the base rubber. If the content of the co-crosslinking agent is 10 parts or more by mass, the hardness of the core becomes appropriate without increasing an amount of the organic peroxide, and thus the resilience of the core becomes better. On the other hand, if the content of the co-crosslinking agent is 55 parts or less by mass, the core does not become too hard and thus the shot feeling becomes better.

As the filler, a filler conventionally formulated in the core of the golf ball can be used. The filler includes, for example, an inorganic filler such as zinc oxide, barium sulfate and calcium carbonate, a high gravity metal powder such as tungsten powder, and molybdenum powder and the mixture thereof. The content of the filler is preferably not less than 0.5 part by mass, more preferably not less than 1 part by mass, and is preferably not more than 30 parts by mass, more preferably not more than 20 parts by mass with respect to 100 parts by mass of the base rubber. If the content is 0.5 part or more by mass, it would be easier to adjust the gravity, while if the content is 30 parts or less by mass, the ratio of the rubber contained in the whole core becomes large and thus the resilience is further improved.

The rubber composition for the core may further include an organic sulfur compound, an antioxidant, or a peptizing agent, as required in addition to the base rubber, the co-crosslinking agent, the crosslinking initiator and the filler. The amount of the antioxidant is not less than 0.1 part and not more than 1 part with respect to 100 parts of the base rubber by mass. The amount of the peptizing agent is not less than 0.1 part and not more than 5 parts with respect to 100 parts of the base rubber by mass.

The core is formed by kneading the above rubber composition and press-molding it into the spherical body in the mold. The conditions for the press-molding should be determined depending on the rubber composition. The press-molding is preferably carried out for 10 to 40 minutes at the temperature of 130° C. to 180° C. under the pressure of 2.9 MPa to 11.8 MPa.

The golf ball body is formed by forming a cover on the core thus obtained from a cover composition.

Examples of the resin component of the cover composition include an ionomer resin and a thermoplastic elastomer. Examples of the ionomer resin are one prepared by neutralizing at least a part of carboxyl groups in a copolymer composed of ethylene and α,β-unsaturated carboxylic acid with a metal ion, or one prepared by neutralizing at least a part of carboxyl groups in a terpolymer composed of ethylene, α,β-unsaturated carboxylic acid and α,β-unsaturated carboxylic acid ester with a metal ion. Examples of the α,β-unsaturated carboxylic acid are acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid. Among them, acrylic acid and methacrylic acid are preferable. Examples of the α,β-unsaturated carboxylic acid ester are methyl ester, ethyl ester, propyl ester, n-butyl ester, isobutyl ester and the like of acrylic acid, methacrylic acid, fumaric acid, maleic acid, and the like. Especially, the ester of acrylic acid and methacrylic acid are preferable. Examples of the metal ion for neutralizing at least a part of the carboxyl groups include monovalent metal ions such as sodium, potassium, and lithium ions; divalent metal ions such as magnesium, calcium, zinc, barium, and cadmium ions; trivalent metal ions such as aluminum ion, or other metal ions such as tin, and zirconium ions. Among them, sodium, zinc, and magnesium ions are preferably used to improve the resilience and the durability.

Examples of the ionomer resin include, but not limited to, HIMILAN 1555, HIMILAN 1557, HIMILAN 1605, HIMILAN 1652, HIMILAN 1702, HIMILAN 1705, HIMILAN 1706, HIMILAN 1707, HIMILAN 1855, and HIMILAN 1856 available from MITSUI-DUPONT POLYCHEMICAL CO.; SURLYN 8945, SURLYN 9945, and SURLYN 6320 available from DUPONT CO.; and IOTEK 8000, and IOTEK 7010 available from Exxon Co. These ionomer resins exemplified above may be used alone, or as a mixture of two or more.

Specific examples of the other thermoplastic elastomers include a thermoplastic polyurethane elastomer having a trade name “Elastollan (e.g. “Elastollan XNY90A, XNY97A, and XNY 585A”) commercially available from BASF Japan Ltd, a thermoplastic polyamide elastomer having a trade name “Pebax (registered trademark) (e.g. “Pebax 2533”)” commercially available from Arkema Inc., a thermoplastic polyester elastomer having a trade name “Hytrel (registered trademark) (e.g. “Hytrel 3548” and “Hytrel 4047”)” commercially available from Du Pont-Toray Co., Ltd., a thermoplastic polystyrene elastomer having a trade name “Rabalon (registered trademark)” commercially available from Mitsubishi Chemical Corporation, and the like.

The cover composition may further contain a pigment. The cover having various color can be obtained. The content of the pigment in the cover composition is 0.01 part by mass or more, more preferably 0.02 part by mass or more, even more preferably 0.03 part by mass or more based on 100 parts by mass of the resin component, and is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, even more preferably 1 part by mass or less based on 100 parts by mass of the resin component. If the content of the pigment is 3 parts by mass or less, the durability of the cover becomes better, and if the content of the pigment is 0.01 part by mass or more, the desired color is obtained. As the pigment, the pigments exemplified for the ink composition can be used.

The cover composition of the present invention may further contain a gravity adjusting agent such as calcium carbonate and barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent brightener or the like to the extent that the performance of the cover is not undermined.

An embodiment for molding a cover is not particularly limited, and includes an embodiment which comprises injection molding the cover composition directly onto the core, or an embodiment which comprises molding the cover composition into a half hollow-shell, covering the core with the two half hollow-shells and subjecting the core with the two half hollow shells to the compression-molding. When preparing a golf ball body by molding a cover, the concave portions called “dimple” are usually formed on the surface. Further, if necessary, the golf ball body is preferably subjected to surface treatments such as deburring, cleaning, and sandblast in order to enhance the adhesion to the mark and the paint film.

After the golf ball body has been prepared, the mark is formed on the surface of the golf ball body using the ink composition. As the method for forming the mark on the surface of the golf ball body, the conventional method can be employed. Examples of the method for preparing the mark are a thermal transfer method where the mark is transferred at the heating condition with the transfer foil, and a pad printing method where the mark is transferred by the transfer pad.

After the mark is formed in such a way with the ink composition, it is preferable to continuously apply a paint and form a paint film. The paint film can be formed by applying the paint composition described above to coat the golf ball body, and drying (or curing). A method for applying the paint composition is not limited. For example, the paint composition is applied to the golf ball with an air-spray gun or by an electrostatic coating method.

Continuously, the paint composition applied to the surface of the golf ball is treated at the temperature of 30° C. to 60° C. for about 1 to 6 hours to form a paint film. The paint film preferably has a thickness of, but not limited to, 5 μm or larger, more preferably 7 μm or larger, and preferably has a thickness of 25 μm or smaller, more preferably 18 μm or smaller. This is because if the thickness is 5 μm or more, the paint film hardly wears off due to continued use of the golf ball, and if the thickness is 25 μm or less, the effect of the dimples becomes large, resulting in better flying performance of the golf ball.

The paint film preferably has a single-layered structure, because the paint applying process can be simplified. Especially, in the present invention, the paint film shows an excellent paint performance (impact resistance) even if the paint film has a single-layered structure. The outer most layer of the paint layer is preferably a clear paint layer.

Although the method for preparing the golf ball is explained based on the embodiment of the two-piece golf ball, the wound core can be used for preparing a wound golf ball, and at least one intermediate layer can be formed between the core and the cover for preparing the multi-piece golf ball including at least three layers. For preparing a wound core golf ball, a conventional wound core can be used in the present invention. The wound core comprises a center and a rubber thread layer which is formed by winding a rubber thread around the center in an elongated state. Examples of the center are a liquid center and a solid center formed of rubber. In the present invention, the rubber thread, which is conventionally used for winding around the center, can be adopted for winding around the center. The rubber thread, for example, is obtained by vulcanizing a rubber composition including a natural rubber, or a mixture of natural rubber and a synthetic polyisoprene, a sulfur, a vulcanization auxiliary agent, a vulcanization accelerator, and an antioxidant. The rubber thread is wound around the center in elongation of about 10 times length to form the wound core.

When preparing a multi-piece golf ball comprising at least three layers, the intermediate layer includes, for example, a thermoplastic resin such as a polyurethane resin, an ionomer resin, Nylon, and a polyethylene; a thermoplastic elastomer such as a polystyrene elastomer, a polyolefin elastomer, a polyurethane elastomer, a polyester elastomer, a polyamide elastomer. Examples of the ionomer resin are one prepared by neutralizing at least a part of carboxyl groups in a copolymer composed of ethylene and α,β-unsaturated carboxylic acid with a metal ion, and one prepared by neutralizing at least a part of carboxyl groups in a terpolymer composed of ethylene, α,β-unsaturated carboxylic acid and α,β-unsaturated carboxylic acid ester with a metal ion. The intermediate layer may further include a filler such as barium sulfate, a colorant such as titanium oxide, and an additive such as a dispersant, an antioxidant, an UV absorbent, a light stabilizer, and a fluorescent brightener, in addition to the base component such as the rubber and the thermoplastic resin.

Presently, in the case of the large size golf ball, the golf ball is required by a rule to be not more than 45.92 g in mass, but there is no limitation on the lower limit. The mass of the golf ball is preferably not less than 44.0 g, more preferably not less than 44.2 g, and is preferably not more than 45.8 g. If the golf ball has a mass of less than 44.0 g, the golf ball loses inertia during the flying and thus loses the speed during the last half of the flying. As a result, the flying distance is lowered. If the golf ball has a mass of more than 45.8 g, the shot feeling becomes heavy.

The golf ball of the present invention preferably has a diameter from 41.0 mm to 44.0 mm, more preferably has a diameter of 42.67 mm or more, which satisfy the specification of the large-size golf ball, and even more preferably about 42.75 mm.

EXAMPLES

The following examples illustrate the present invention, however these examples are intended to illustrate the invention and are not to be construed to limit the scope of the present invention. Many variations and modifications of such examples will exist without departing from the scope of the inventions. Such variations and modifications are intended to be within the scope of the invention.

[Evaluation Method] (1) Luster (Brilliance)

The golf balls where the mark was formed were visually observed and evaluated according to the following criteria.

E(Excellent): The luster was even more sharply observed. G(Good): The luster was sharply observed. F(Fair): The luster was slightly observed (allowable range). P(Poor): The luster was not observed.

(2) Visibility

The golf ball having a mark thereon was located on the grass in a fine weather. Ten golfers approached the golf ball gradually from the position which was 50 m away from the golf ball, and registered the distance between the golf ball and the position where the golfer recognized the existence of the mark on the golf ball. The distances of the ten golfers were averaged and regarded as the result of each golf ball.

(3) Impact Resistance of the Mark

Each golf ball was hit 100 times repeatedly with a driver (W#1) attached to a swing robot manufactured by TRUETEMPER CO, at the head speed of 45 m/sec. The durability was evaluated by observing the peeled condition of the mark based on the following criteria.

E(Excellent): The mark did not peel off. G(Good): The area where the mark peeled off was not more than 1 mm². F(Fair): The area where the mark peeled off was more than 1 mm² to 4 mm² (allowable range). P(Poor): The area where the mark peeled off is more than 4 mm².

(4) Impact Resistance of the Paint Film

Each golf ball was hit 100 times repeatedly with a driver (W#1) attached to a swing robot manufactured by TRUETEMPER CO, at the head speed of 45 m/sec. The durability was evaluated by observing the peeled condition of the paint film based on the following criteria.

E(Excellent): The paint film did not peel off. G(Good): The area where the paint film peeled off was less than 1 mm². F(Fair): The area where the paint film peeled off was not less than 1 mm² and less than 4 mm² (allowable range). P(Poor): The area where the paint film peeled off is not less than 4 mm².

(5) Color Developing Property

With respect to the golf balls No. 12 to No. 22, L* value, a* value, and b* value of the portion where the mark is not formed were measured using a color difference meter named “CR-221” manufactured by MINOLTA CO using a pulse xenon lamp as a light source. The brightness L* and the vividness C*=(a*²+b*²)^(1/2) were determined to evaluate the color developing property. The “L*” value is an index of brightness. A larger “L*” value indicates a brighter color, and a smaller “L*” value indicates a darker color. The vividness C* is an index of vividness. A larger “C*” indicates a more vivid color and smaller “C*” indicates a more dull color.

[Production of the Golf Balls] (1) Preparation of Solid Core

The rubber composition shown in Table 1 was kneaded and pressed in upper and lower molds each having a spherical cavity at the heating condition of 160° C. for 13 minutes to obtain the solid core in a spherical shape having a diameter of 39.3 mm.

TABLE 1 Core formulation Amount (parts) Polybutadiene rubber 100 Zinc oxide 5.6 Zinc acrylate 22.0 Calcium carbonate 21.0 Dicumyl peroxide 1.85 Note on Table 1: Polybutadiene rubber: BR-11 (cis content: 96%) available from JSR Co. Zinc acrylate: “ZNDA-90S” produced by NIHON JYORYU KOGYO Co,. LTD. Zinc oxide: “Ginrei R” produced by Toho-Zinc Co. Calcium carbonate: Bihoku Funka Kogyo Co., Ltd. Dicumyl peroxide: “Percumyl D” produced by NOF Corporation

(2) Preparation of the Cover Material

The materials shown in Table 2 were mixed using a twin-screw kneading extruder to obtain the cover composition in the form of pellet. The extrusion was conducted in the following conditions:

screw diameter=45 mm, screw revolutions=200 rpm, screw L/D=35, and

the cover composition was heated to from 200° C. to 260° C. at the die position of the extruder.

TABLE 2 Cover formulation Amount (parts) HIMILAN 1605 40 HIMILAN 1706 30 HIMILAN 1707 30 Titanium oxide 2 Notes on Table 2: HIMILAN 1605: an ionomer resin of a sodium ion-neutralized ethylene-methacrylic acid copolymer, available from MITSUI-DUPONT POLYCHEMICAL CO., LTD. HIMILAN 1706: an ionomer resin of a zinc ion-neutralized ethylene-methacrylic acid copolymer, available from MITSUI-DUPONT POLYCHEMICAL CO., LTD. HIMILAN 1707: an ionomer resin of a sodium ion-neutralized ethylene-methacrylic acid copolymer, available from MITSUI-DUPONT POLYCHEMICAL CO., LTD.

(3) Preparation of the Golf Ball Body

The cover composition thus prepared was directly injection-molded onto the core to form the cover, thereby obtaining the two-piece golf ball having a diameter of 42.7 mm. The upper and lower molds for forming the cover have a spherical cavity with dimples. The part of the dimples can serve as a hold pin which is retractable. When forming the golf ball body, the hold pins were protruded to hold the core, and the resin heated at 210° C. was charged into the mold held under the pressure of 80 tons for 0.3 seconds. After the cooling for 30 seconds, the molds were opened and then the golf ball body was discharged.

(4) Printing a Mark and Forming a Paint Film

As shown in tables 3 and 4, the ink composition for the mark was prepared. The mark “X” of width 8 mm, height 8 mm, line width 2 mm was printed by the pad stamp. Then, the clear paint comprising a two-component curing type polyurethane as a base material was prepared. The base resin of this paint was a mixture of a polyether polyol and a polyester polyol. The base resin has a hydroxyl value of 82 mgKOH/g. The curing agent of this paint was hexamethylene diisocyanate. This paint has a NCO/OH ratio of 1.2/1.0. This paint was applied to the cover with an air spray gun. The paint was dried in the oven heated at 40° C. for 120 minutes to form the paint film having a thickness of about 10 μm.

The obtained golf balls were evaluated with respect to the mark and the paint film, and the results thereof were shown in Tables 3 and 4. The evaluation of the mark was conducted only for golf balls No. 1 to No. 11, No. 22, and the evaluation of the paint film was conducted only for golf balls No. 12 to No. 22.

TABLE 3 Golf ball No. 1 2 3 4 5 6 7 8 9 10 11 Ink composition Base resin 71.5 71.5 69 69 63 63 57.5 57.5 64.5 35 35 Curing agent 1.5 1.5 7 7 1 1 1 1 2.5 1 1 Solvent 13.5 13.5 4.5 4.5 10 10 9 9 20 46.8 46.8 Flatting agent 4.5 4.5 5 5 3 3 3 3 7 4 4 Pigment (phthalocyanine blue) 4 4 4.5 4.5 3 3 2.5 2.5 6 3.2 3.2 Luster material 1 5 — 10 — 20 — 27 — — — — Luster material 2 — 5 — 10 — 20 — 27 — — — Luster material 3 — — — — — — — — — 10 — Luster material 4 — — — — — — — — — — 10 Paint Urethane resin 100 100 100 100 100 100 100 100 100 100 100 Composition Luster material 1 — — — — — — — — — — — Luster material 2 — — — — — — — — — — — Luster material 3 — — — — — — — — — — Mark Luster G G E E E E E E P G G Evaluation Visibility(m) 14 14.1 14.6 14.5 15.3 15.3 15.8 15.9 6.4 12.8 13.4 Impact resistance E E G G G G F F E F F Ink composition, Paint composition: parts by mass Urethane resin: Two component curing type urethane resin

TABLE 4 Golf ball No. 12 13 14 15 16 17 18 19 20 21 22 Ink composition Base resin 64.5 64.5 64.5 64.5 64.5 64.5 64.5 64.5 64.5 64.5 69 Curing agent 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 7 Solvent 20 20 20 20 20 20 20 20 20 20 4.5 Flatting agent 7 7 7 7 7 7 7 7 7 7 5 Pigment (phthalocyanine blue) 6 6 6 6 6 6 6 6 6 6 4.5 Luster material 1 — — — — — — — — — — 10 Luster material 2 — — — — — — — — — — — Luster material 3 — — — — — — — — — — — Luster material 4 — — — — — — — — — — Paint Urethane resin 100 100 100 100 100 100 100 100 100 100 100 Composition Luster material 1 0.5 — 2.5 — 10 — — 0.01 25 — 2.5 Luster material 2 — 0.5 — 2.5 — 10 — — — — — Luster material 4 — — — — — — — — — 10 — Mark Luster — — — — — — — — — — E Evaluation Visibility(m) — — — — — — — — — — 14.8 Impact resistance — — — — — — — — — — G Paint Luster G G E E E E P P E G E Evaluation Impact resistance G G G G F F G G P F G Color Development/L* value 92 92 91 91 90 90 93 92 88 88 91 Color Development/C* value 14 14 13 13 12 12 14 14 9 9 13 Ink composition, Paint composition: parts by mass Urethane resin: Two component curing type urethane resin

As the ink composition, the following base resin, curing agent, solvent, and luster materials were used.

Base resin: two-component curing type “EPH-00 medium” (epoxy resin, solid content: 20 mass % to 60 mass ° A)) available from Navitas Corporation Curing agent: Hexamethylene diisocyanate Solvent: a mixture of 50 mass % methoxymethylbutylacetate, 20 mass % acetylacetone, 6 mass % propyleneglycol monomethylether acetate, 4 mass % ethylacetate, 20 mass % an aromatic hydrocarbon Luster material 1: “Firemist Colormotion Ruby (transparent base: glass flake of borosilicate glass, First transparent layer: TiO₂, Second transparent layer: SiO₂, Third transparent layer: TiO₂) available from BASF Co. Luster material 2: “Firemist Colormotion Topaz (transparent base: glass flake of borosilicate glass, First transparent layer: TiO₂, Second transparent layer: SiO₂, Third transparent layer: TiO₂) available from BASF Co. Luster material 3: Aluminum flake (average particle size 11.6 μm, thickness of 20 angstrom) Luster material 4: “Iriodin 100” available from MERCK, mica coated with one titanium oxide layer, average particle size: 10 μm to 60 μm

The golf balls No. 1 to No. 8 are the golf balls where the mark was formed with the ink composition comprising the luster material. All of the golf balls were excellent in the luster and visibility with respect to the mark. The comparison among the golf balls No. 1 to No. 8 indicated that the luster becomes stronger as the content of the luster material is increased. Especially, the excellent luster was obtained when the content of the luster material was 10 mass % or more. On the other hand, it was found that the impact resistance tends to be lower if the content of the luster material is excessively high.

The golf ball No. 9 is the case that the ink composition for printing the mark did not contain the luster material. The luster was not observed for the golf ball No. 9. The golf balls No. 10 and No. 11 are the cases that the ink compositions contained aluminum flake and mica coated with titanium oxide as the luster material. The luster was observed for the golf balls No. 10 and No. 11, but the visibility thereof was low compared to the golf balls No. 1 to No. 8.

The golf balls No. 12 to No. 17 are the golf balls where the paint film contained the luster materials. All of the golf balls were excellent in the luster and impact resistance with respect to the paint film. The comparison among the golf balls No. 12 to No. 17, 19, and 20 indicated that the luster becomes stronger as the content of the luster material is increased. On the other hand, it was found that the impact resistance tends to be lower if the content of the luster material is excessively high.

The golf ball No. 18 is the case that the paint film did not contain the luster material. The luster was not observed for the golf ball No. 18. The golf ball No. 21 is the case that the paint film contained mica coated with titanium oxide as the luster material. The excellent luster was not observed for the golf ball No. 21, even though the content of the luster material was 10 mass % or more. Further, the impact resistance was lowered.

In addition, the golf balls No. 12 to No. 17 had higher brightness L* and vividness C* than the golf ball No. 21 containing mica coated with titanium oxide as the luster material. That is, the golf balls of the present invention had covers having a bright and vivid color, and were excellent in the color developing property, compared to the golf ball No. 21 using the base material having a low transparency or opacity.

The golf ball No. 22 is the case that both of the mark and the paint film contained the luster material. The golf ball No. 22 is excellent in the luster, visibility and the impact resistance of the mark as the golf ball No. 3, and excellent in the luster, impact resistance and color developing property of the paint film as the golf ball No. 14. These results indicates that the case that both of the mark and the paint film contained the luster material gave the similar results to the case that either of the mark and the paint film contained the luster material. Especially, the visibility of the mark was improved compared to the golf ball No. 3 using the same ink composition.

The present invention can be preferably applied to a golf ball having an individualized and improved appearance by imparting the luster. This application is based on Japanese Patent application No. 2009-121355 filed on May 19, 2009, the contents of which are hereby incorporated by reference. 

1. A golf ball comprising a golf ball body, a mark formed on a golf ball body, a paint film coating the golf ball body and the mark, wherein the mark and/or the paint film contains a luster material, wherein the luster material has a core material having a transparent base and a first transparent layer formed on the transparent base; and at least one composite layer formed on the core material and consisting of a second transparent layer having a lower refractive index than the first transparent layer, and a third transparent layer having a higher refractive index than the second transparent layer.
 2. The golf ball according to claim 1, wherein materials constituting the first transparent layer and the third transparent layer are at least one selected from the group consisting of titanium dioxide, iron oxide, zirconium dioxide, zinc oxide, zinc sulfide, and bismuth oxychloride.
 3. The golf ball according to claim 1, wherein a material constituting the second transparent layer is selected from the group consisting of silicon dioxide, magnesium fluoride, and aluminum oxide.
 4. The golf ball according to claim 1, wherein the transparent base is a glass flake.
 5. The golf ball according to claim 1, wherein the first transparent layers are directly formed on the both faces of the transparent base, and the second transparent layers are directly formed on the first transparent layers, and the third transparent layers are directly formed on the second transparent layers.
 6. The golf ball according to claim 1, wherein the transparent base has a light transmittance of at least 75%.
 7. The golf ball according to claim 1, wherein materials for the first transparent layer, the second transparent layer, and the third transparent layer are selected so that a difference of a refractive index between adjacent layers is at least 0.2.
 8. The golf ball according to claim 1, wherein the first transparent layer, the second transparent layer, and the third transparent layer each has a thickness ranging from 40 nm to 250 nm.
 9. The golf ball according to claim 1, wherein the luster material has an average particle size ranging from 5 μm to 300 μm.
 10. The golf ball according to claim 1, wherein the luster material has a thickness ranging from 0.5 μm to 5 μm.
 11. The golf ball according to claim 1, wherein the mark is formed from an ink composition containing the luster material in an amount ranging from 1 mass % to 30 mass %.
 12. The golf ball according to claim 11, wherein the ink composition comprises a pigment in an amount ranging from 0.5 mass % to 20 mass %.
 13. The golf ball according to claim 12, wherein a content ratio of the luster material to the pigment (luster material [mass %]/pigment [mass %]) ranges from 0.1 to
 50. 14. The golf ball according to claim 11, wherein the ink composition contains a base resin in an amount ranging from 15 mass % to 50 mass %.
 15. The golf ball according to claim 14, wherein the ink composition comprises a polyester resin, an epoxy resin, a soluble nitrocellulose, an acrylic resin, a vinyl chloride-vinyl acetate copolymer, an urethane resin, or a polyamide resin as the base resin.
 16. The golf ball according to claim 11, wherein the ink composition contains non-volatiles in an amount ranging from 20 mass % to 70 mass %.
 17. The golf ball according to claim 1, wherein the paint film contains an acrylic resin, an epoxy resin, a polyurethane resin, a polyester-based resin, or a cellulose-based resin as a resin component.
 18. The golf ball according to claim 17, wherein the paint film contains the luster material in an amount ranging from 0.05 part to 20 parts by mass with respect to the resin component. 